1. Field of The Invention
The present invention relates to a method and apparatus for recording and reproducing a sampled-analog color video signal; and to recordings produced by such method and apparatus. More particularly, it relates to such method and apparatus for recording and reproducing wherein samples comprising the signal are assigned to respective channels of a plurality of channels. The information in the channels is recorded on a plurality of parallel tracks--one track per channel--on a recording medium.
2. Discussion Relative to The Prior Art
Recently, solid state color image sensing arrays have been proposed that make highly efficient use of the individual picture sensing elements of the arrays by selectively sensitizing the elements to respective wavelengths of light, the number of elements thus sensitized to a particular wavelength being proportioned on the basis of human visual acuity at such wavelengths. See, for example, U.S. Pat. No. 3,971,065 issued July 20, 1976 to Bayer and U.S. Pat. No. 4,047,203 issued Sept. 6, 1977 to Dillon. The outputs of such arrays are sampled analog color video signals composed of successive groups of color samples, such groups representing successive rows or lines of a video field or frame. If the problem of providing a relatively low-cost recorder could be solved, these solid state color image sensors would lend themselves nicely to the design of a minimum-cost, mass-produced, color video camera/recorder for the consumer market.
Although video recording and reproduction is well known, video tape recorders that are presently priced within the range of the consumer market employ the concept of a rotating magnetic head for recording a television signal on magnetic tape. The rotary head mechanism provides a very high density, relatively wide bandwidth recording by rapidly rotating a magnetic head(s) relative to the tape to produce many parallel tracks disposed generally across the width of the tape. While the rotating head concept achieves the goal of high density, large bandwidth recording, it does so at the expense of a requirement for precision parts in the rotary head mechanism and tape transport system resulting in relatively high manufacturing costs for a rotary head recording system.
It has long been appreciated that the simplicity of an "essentially-fixed" head design for video tape recording and playback apparatus could result in very desirable manufacturing economies. "Essentially-fixed" as used herein means non-rotating, some movement of the recording head, such as toward and away from the recording medium, or to and from in the direction of relative head-to-medium travel, is contemplated within the meaning of "essentially-fixed".
The most straightforward approach to a fixed head video tape recorder design would appear to be one in which the recording tape is moved past an essentially-fixed magnetic recording head at a speed sufficiently high to accommodate the relatively wide bandwidth video signal, e.g., approximately three meters per second for a standard NTSC color television signal. Although such systems have been implemented, they require high speed precision operating mechanisms for their tape transports, and relatively long lengths of tape stored on large reels for producing programs of reasonable length, and hence are impractical for a product aimed at the consumer market.
In a variety of prior art essentially-fixed head systems, the relative head/tape speed is reduced by separating the video signal into a number of component parts and assigning the parts to a corresponding number of channels. The signal components in the channels are then recorded on a corresponding number of parallel tape tracks by means of a multichannel essentially-fixed recording head. In some such prior art systems employing "time-division-demultiplexing" (e.g. U.S. Pat. No. 2,952,745 issued Sept. 13, 1960 to Walker), a video signal is periodically sampled, the samples are demultiplexed into a number of channels, and the signal portions in the channels are recorded on a corresponding number of tracks on a recording medium by a multichannel essentially-fixed recording head. For N channels, the bandwidth per channel is thereby reduced by a factor of 1/N. As few as two to as many as 600 channels have been suggested in prior art demultiplexing schemes; see U.S. Pat. No. 3,975,764 issued Aug. 17, 1976 to Kobayashi et al. In such prior art time-division-demultiplexing systems, a relatively large amount of power, at the sampling frequency, is introduced into the channels. This power at the sampling frequency tends to interfere with efficient recovery of the original signal from the recording and may result in a final signal of degraded quality.
In another prior art recording system, as shown in U.S. Pat. No. 3,502,795, issued Mar. 24, 1970 to M. Camras, the video signal is separated into components according to red, green, and blue colors, and each color component is recorded onto a separate track. Because there is more useful information in the green component of the signal, the green track is wider than the red or blue tracks. To increase the recording density on the recording medium and hence the playing time, the direction of tape transport is repeatedly reversed while shifting the lateral position of the recording head to thereby increase the total number of parallel tracks on the tape. During each tape reversal, the picture may be momentarily disrupted.
Although multi-track essentially-fixed-head recording would appear to offer substantial cost benefits for use in a color-video camera/recorder for the consumer market, to date, none of the prior art essentially-fixed head, multi-track recording schemes have proven commercially successful.